1. Field of the Invention
Embodiments of the present invention relate to systems and methods for polymer melt characterization and elastomer testing using a rheometer. More particularly, embodiments of the present invention relate to systems and methods for measuring the extensional properties of a polymer melt or elastomer sample on a rotational rheometer.
2. Background Information
Extensional measurement instruments are used to measure the viscosity and stress relaxation of samples including polymers, elastomers, and rubber compounds. These instruments are also useful in optimizing the throughput of material processing operations. These operations include fiber spinning, film blowing, blow molding, and sheet casting. Extensional measurement instruments are referred to as extensional rheometers. U.S. Pat. No. 6,578,413 to Sentmanat (the '413 patent) describes different extensional rheometers that have been developed in the prior art.
Dedicated extensional rheometers, however, are cost prohibitive, difficult to use, and have limited utility. As a result, fixtures have been developed that allow extensional measurements to be made using commercial rotational rheometers. The '413 patent describes an extensional rheometer fixture. This fixture includes a drive shaft connected to an armature. The armature is further connected to a torque shaft, and two rotatable drums are mounted in the armature. One end of a sample is connected to each drum. Both drums are rotated, stretching the sample. The torque in the fixture caused by the stretching of the sample is measured.
One problem with the fixture described in the '413 patent is the effect that the friction in the bearings of both drums and the friction in the gearing mechanism of both drums have on the measurement of torque. Because of this friction, the torque cannot be measured directly. Instead, the torque on the sample must be calculated from the measured torque and the effects of the friction.
In view of the foregoing, it can be appreciated that a substantial need exists for systems and methods that can advantageously allow extensional measurements to be made more directly using commercial rotational rheometers.